1.1 Introduction
Renewable energy sources have been with humanity since time immemorial. The burning of biomass has been a source of heat. Wind energy has been used to power boats and sailing rafts, to transport water to elevated or more distant agricultural areas, and lastly to produce flour in windmills with initially vertical and, as technology developed, horizontal axes. When analysing the physical basis of photovoltaics, it is important to consider that this type of energy production has a source outside the Earth. Fortunately, from the point of view of humanity, the Sun is an inexhaustible supply of energy. However, it has one disadvantage that must be taken into account, i.e., it provides energy only to the side of the Earth that happens to be facing the Sun. This means that electricity can be produced only during the daytime and with varying intensity depending on the time of day. There is also a dependence on the geographical location of the power plant due to differences in insolation. The photovoltaic phenomenon was discovered in the 19th century by Alexander Edmond Becquerel (1839). However, it found real application only after World War II with the rapid development of electronics and semiconductor materials (in the initial phase of space and military applications). In particular, it was the competition and the space race that pushed the development of photovoltaics significantly forward, as solar cells provided a lightweight (cost of transport to orbit) and inexhaustible (constant access to solar energy) source of electricity to power satellite equipment. The first post-war energy crisis of the mid-1970s and the Club of Rome's Report on the Depletion of Earth's Fossil Resources focused public attention on renewable energy issues. Sources such as hydroelectric power plants, wind power plants, and finally photovoltaic power plants have become the subject of analysis by engineers, designers, and economists all over the world.
Hydroelectric power is an investment that takes decades (just filling the reservoir took more than 18 years in Colorado, for example). High-capacity wind turbines (individual windmills range from 2 to 10 MW) face protests from environmentalists due to their environmental impact and bird migration. Photovoltaics, however, is an attractive alternative to conventional energy sources as mentioned above, because electricity is obtained directly from solar energy without noise, pollution and other factors causing adverse environmental changes. The almost unlimited demand for monocrystalline silicon of the electronics industry limited the development of photovoltaics in the second half of the 20th century. Only the transfer of many technologies to China, especially the vacuum Czochralski technology for the production of monocrystalline silicon, became the beginning of the exponential development of photovoltaics in the first two decades of the 21st century. Every dynamic development attracts the attention of researchers and engineers. This was also the case with photovoltaics. A number of modifications have significantly increased the energy conversion efficiency of monocrystalline photovoltaic cells. A method of relatively inexpensive production of polycrystalline silicon for making photovoltaic cells has been developed. Semiconductor research has led to the application of a number of new semiconductor materials for photovoltaic cell manufacturing. Thin-film technology, in which material consumption is a hundred times less than in silicon cells, has proven particularly promising. And the last 10 years have seen the introduction of low-cost materials like perovskites and polymers into the photovoltaic field.
The dynamic development of photovoltaic installations and research has, in many cases, preceded long-term educational cycles. Hence the need for publications that provide a source of knowledge and information for an ever-widening circle of people involved in the development of the photovoltaic industry: materials engineers, power engineers all the way to the end consumers of electricity. At this point, we should pay tribute to Prof. Jan Stopczyk who created the concept and philosophy of the prosumer, i.e., the producer and consumer of micro-scale electricity at the same time. However, this individual contribution multiplied by millions of prosumers becomes a serious contribution to the national energy system. No one has the slightest doubt that after the depletion of fossil fuels humanity will have no cheaper alternative to renewable energy sources, especially photovoltaics. The rapid growth of photovoltaic production and installation has led to a drastic drop in energy prices per kWp from photovoltaic sources, which had previously been a major barrier to the development of installations.
This book is intended primarily for students studying renewable energy sources, including photovoltaics, but also for anyone interested in learning about photovoltaics, its development and prospects. It does not constitute instructional material for photovoltaic installers, since such materials are already available in bookstores. The electronic form of the textbook was chosen because of the change in the way the material can reach the student and the reader as well as the possibility of making modifications to the content resulting from the dynamic changes occurring in this developing field of technology.
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How dynamic changes are taking place in the world in the field of renewable energy sources, including photovoltaics, can be seen by observing the changes taking place in the continuously increasing share of these sources in energy production. A comparison of countries which in the last decade have seen a very strong increase in installed photovoltaic capacity does not correspond to the location of the sunniest areas of the globe. Presently, it is the political decisions about the methods of subsidizing PV installations or energy storage that are the basis of the installation dynamics. The second factor is major investments in the expansion of the PV industry such as China's dominance in silicon substrate production. When comparing 2010, when almost the entire installed capacity bar was occupied by Europe, to the latest data from 2019, one can see how colossal the changes have been ( Fig. 1 ) [1]. The installed capacity in countries such as China, the USA, Japan and the rest of the world has overtaken that of Europe many times over. The installed capacity is still far from being sufficient to cover the entire energy needs of the world. However, the dynamics of change indicates that many countries understand the dangers of \( CO_{2} \) and the role that renewable energy sources play because of climate conditions and in the global energy mix.